Field of the Invention
The present invention relates to an additive gas delivery apparatus for delivery of additive gas to a patient. In particular, the invention relates to a nitric oxide (NO) delivery apparatus for delivery of NO to a patient in need of NO therapy. The invention also relates to a gas delivery system and a method for monitoring delivery of additive gas to a patient.
Description of the Prior Art
In conjunction with respiratory care of a patient provided by means of a breathing apparatus, such as a ventilator, respirator or Anaesthesia machine, the physician may sometimes wish to supplement the breathing gas with an additive gas having a desired medical effect on the patient. Nitric oxide (NO), also known as nitrogen monoxide, is an example of such an additive gas.
In small quantities, NO can have several beneficial effects on the pulmonary function of a subject. In particular, NO has a vasodilating effect and prompt supply of NO may be life critical to patients suffering from vascular spasms in the pulmonary capillaries.
In existing NO delivery systems it is normally up to the operator to ensure that NO is delivered to the patient connected to the NO delivery system by correctly interpreting state feedback provided to the operator via a user interface of the treatment device or a monitoring system monitoring the treatment currently being provided to the patient. This setup is sensitive to mistakes and misunderstandings, sometimes leading to situations where activation of NO therapy is forgotten or where NO therapy is accidentally interrupted.
This risk is particularly prominent for system setups where a standalone NO delivery apparatus is connected to a ventilator circuit to deliver a flow of NO into a flow of breathing gas that is to be supplied to a ventilated patient. Since the NO delivery apparatus typically has to be activated manually and independently of the ventilator in order to start delivering NO, there is a risk that the system operator, after having activated and configured the ventilator, forgets to activate the NO delivery apparatus.
Although critical to patient safety, this problem is not addressed by known NO delivery systems according to prior art. Instead, NO delivery systems according to prior art rather focus on the problem of how to avoid formation and delivery of highly toxic nitrogen dioxide, NO2, to the patient, which is a delicate problem since NO is converted into NO2 over the course of time when in contact with oxygen containing gas, such as air.
For example, EP937479 discloses an NO delivery system including certain functions to provide protection against the inadvertent formation of NO2 through the reaction of NO and O2 within the device itself. This is partly achieved by functionality for detecting attempts to inhale by the patient and, if attempts to inhale cannot be detected for a certain period of time, e.g. 15 seconds, the system will automatically deliver a pulse of NO so that the device purges itself and rids the possible formation of any NO2 that may have formed since the last pulse of NO was administered. Another feature of the proposed NO delivery system is the activation of an alarm to alert the user of a situation in which no attempts to inhale has been made by the patient during a predetermined period of time, alerting the user to the situation to take prompt action to determine the problem.
U.S. Pat. No. 6,962,154 also discloses an NO delivery system, which system includes functionality for purging itself with one or more other gases to avoid delivery of NO2 to the patient.
U.S. Pat. No. 6,125,846 is yet another document describing an NO delivery system equipped with purging functionality to avoid administration of NO2 to a patient. Here, to avoid formation and administration of NO2 after interruption in NO administration, the system comprises means for sensing the commencement of an active state in which the system is capable of delivering NO containing gas to a patient, and for purging the system with NO containing gas during a predetermined period of time when the commencement of an active state is sensed.
Thus, there are several disclosures of NO delivery systems addressing the problem of how to mitigate the risk of formation and unintentional administration of NO2. However, there are no known NO delivery systems addressing the problem of how to minimize the risk of unintentional non-delivery of NO to patients in NO delivery systems.
As mentioned above, unintentional non-delivery of NO to a patient in need of NO therapy is a life-threatening situation. To avoid such situations there is thus a need for a safer and more user-friendly NO delivery system.